On the Geology of the neighbourhood of Grantham. 53 



Further on sonic inferior strata are visible, viz. : — ft. in. 



9. Sand 4 



10. Ferrnginow oolite 14 



11. Clay 



Total 36 6 



The beds seem to be nearly horizontal. 



The best slate splits into thin lamina?, and forms a beautiful 

 and useful material for roofing, preferable even in some respects 

 to that oi* the- Cotswolds, being finer-grained and more micaceous ; 

 but the average thickness of the whole is about the same. There 

 is however a sufficient lithological resemblance to identify this 

 formation in Northamptonshire with that of Gloucestershire and 

 Oxfordshire; and even the minor details are more nearly alike 

 than the distance of one deposit from the other would lead us to 

 suppose. The formation, however, near Stamford is by no means 

 so extensive in its geographical range, being, as far as I am aware, 

 limited to a few localities in that neighbourhood. I was unable 

 to trace the junction of the slate with either the Great Oolite 

 above, or the Inferior Oolite below, but it may be observed (ac- 

 cording to Mr. Morris) in one or two places in this district. I 

 cannot state positively whether it is as closely connected with the 

 Great Oolite as it is in the Cotswolds, where my friend Professor 

 Buckman and myself (in a joint paper on the Stonesfield Slate 

 of Gloucestershire*) conceive it to be not sufficiently distinguish- 

 able from it to entitle it to rank as an independent formation. 

 But from the facts and sections given in Mr. Morris's paper, 

 they seem to be as closely intermingled; indeed he distinctly 

 states that the slate is not independent of the Great Oolite, and 

 thus confirms our views respecting its characters in Gloucester- 

 shire. The bed of clay, which we suppose to be the representative 

 of the ' Bradford clay/ does not occur at Collyweston overlying 

 the slate, though it may have been previously denuded. 



Fossils generally are not very abundant in the Collyweston 

 slate, and these consist almost entirely of marine shells, among 

 which Trigonia impressa (a highly characteristic shell), Gervillia 

 acuta (a gregarious species, lying grouped together on the slabs, 

 but not common in the Cotswolds), Cardium, Pinna, Pecten, and 

 a small Natica, are the most frequent, though a few others are 

 mentioned by Mr. Morris. He also notices numerous frag- 

 ments of Pecopteris poh/podioides, a species of fern abundant in 

 the oolitic shales of Yorkshire, which seems to identify the slate 

 with them. Plants however, as far as my observation went, are 

 comparatively rare at Collyweston, and very imperfect. I walked 

 over tons of slate laid out for weathering, as in Gloucestershire, 

 and I could not observe even a trace of vegetable matter, the 

 slate being in most cases particularly unfossiliferous, and on this 



* See Quarterly Journal of the Geological Society, No. II. p. 220. 



o 



